1. Technical Field
Some example embodiments generally relate to an image forming apparatus and/or a fixing device, for example, for fixing a toner image on a recording medium.
2. Description of Background Art
A background image forming apparatus, for example, a copying machine, a facsimile machine, a printer, or a multifunction printer having copying, printing, scanning, and facsimile functions, forms a toner image on a recording medium (e.g., a sheet) according to image data by an electrophotographic method. For example, a charger charges a surface of an image carrier (e.g., a photoconductor). An optical writer emits a light beam on the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to image data. The electrostatic latent image is developed with a developer (e.g., toner) to form a toner image on the photoconductor. A transfer device transfers the toner image formed on the photoconductor onto a sheet. A fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image on the sheet. The sheet bearing the fixed toner image is output onto the outside of the image forming apparatus.
The fixing device generally includes a pressing roller and/or a fixing roller. The pressing roller and the fixing roller oppose each other to form a nip between the pressing roller and the fixing roller. While the pressing roller and the fixing roller nip a sheet bearing a toner image, the pressing roller and the fixing roller apply pressure and heat to the sheet bearing the toner image to fix the toner image on the sheet. Alternatively, the fixing device may include a fixing belt instead of the fixing roller.
FIG. 1 illustrates an example background fixing device 41RA using a belt method. In the fixing device 41RA, a fixing belt 103 is looped over a fixing roller 102 and a heating roller 104. The fixing roller 102 opposes a pressing roller 101 via the fixing belt 103. A tension applier 107 includes a spring 108 and/or a roller 109 and applies tension to the fixing belt 103 at a position between the fixing roller 102 and the heating roller 104. The heating roller 104 includes a heater 105 and heats the fixing belt 103. The pressing roller 101 presses the fixing roller 102 via the fixing belt 103 to form a nip between the pressing roller 101 and the fixing belt 103. While the pressing roller 101 and the fixing belt 103 nip a sheet P bearing a toner image, the pressing roller 101 and the fixing belt 103 apply pressure and heat to the sheet P to fix the toner image on the sheet P. A separator 106 separates the sheet P bearing the fixed toner image and fed by the pressing roller 101 and the fixing belt 103 in a direction C from the fixing belt 103. A thermistor 110 detects a temperature of the fixing belt 103.
FIG. 2 illustrates another example background fixing device 41RB using a SURF method (e.g., a film method). In the fixing device 41RB, a ceramic heater 113 opposes a pressing roller 111 via a fixing belt 112 having an endless belt shape. A holder 114 holds the ceramic heater 113. A support 115 supports the holder 114. The pressing roller 111 presses the ceramic heater 113 via the fixing belt 112 to form a nip between the pressing roller 111 and the fixing belt 112. The ceramic heater 113 heats the fixing belt 112 at the nip.
FIG. 3 illustrates yet another example background fixing device 41RC using a roller method. In the fixing device 41RC, a pressing roller 121 presses a fixing roller 122 to form a nip between the pressing roller 121 and the fixing roller 122. A heater 123 is provided inside the fixing roller 122 having a thin thickness.
Image forming apparatuses may need to shorten a warm-up time period needed to increase the temperature of the image forming apparatus up to a reference temperature at which a print operation is properly performed after the image forming apparatus is powered on. Image forming apparatuses may also need to shorten a first print time period needed for the image forming apparatus to finish outputting a sheet bearing a fixed toner image onto the outside of the image forming apparatus after the image forming apparatus receives a print request. Image forming apparatuses may also need to form a toner image on a sheet at a higher speed.
When the fixing device 41RA (depicted in FIG. 1) is provided in a high-speed image forming apparatus, the fixing belt 103 may rotate at a high speed. Therefore, an increased amount of heat may be radiated at a portion of the fixing belt 103 other than the nip, resulting in faulty fixing.
The fixing device 41RB (depicted in FIG. 2) has a decreased heat capacity compared to the fixing device 41RA (depicted in FIG. 1) and thereby is quickly heated with a compact structure. However, the ceramic heater 113 heats the fixing belt 112 at the nip only. Heat is easily drawn from the fixing belt 112 to a sheet bearing a toner image and having a decreased temperature at an entrance to the nip, resulting in faulty fixing. In the fixing device 41RB, the holder 114 and the support 115 are provided inside a loop formed by the fixing belt 112. The holder 114 and the support 115 having an increased heat capacity absorb heat generated by the ceramic heater 113, resulting in a decreased thermal conversion efficiency. When the rotating fixing belt 112 moves away from the ceramic heater 113, forced convection cools the fixing belt 112, resulting in a decreased thermal conversion efficiency.
In the fixing device 41RA or 41RB, the rotating fixing belt 103 or 112 may move in a thrust direction to collide with a stopper, and may be damaged. When a user removes a jammed sheet from the fixing device 41RA or 41RB, a force is applied to the fixing belt 103 or 112. When the applied force bends the fixing belt 103 or 112, a small or large kink is formed on the fixing belt 103 or 112. The small kink may break the fixing belt 103 or 112. The large kink may appear as a faulty toner image on a sheet when a fixing operation is performed.
The fixing device 41RC (depicted in FIG. 3) having a simple structure has a decreased heat capacity. However, a center of curvature of the nip faces a toner image on a sheet nipped by the pressing roller 121 and the fixing roller 122. Therefore, the sheet is adhered around the fixing roller 122 via the toner image. The fixing device 41RC may include a separator (e.g., a nail, a plate, and/or the like) for preventing the sheet from adhering around the fixing roller 122. However, the separator needs to apply an increased force to the sheet and the fixing roller 122 to separate the sheet from the fixing roller 122. The separator may scrape the toner image on the sheet, resulting in a faulty toner image on the sheet.